Aerial image acquisition method and system for investigating traffic accident site by unmanned aerial vehicle

ABSTRACT

Disclosed are an aerial image acquisition method and a system for investigating a traffic accident site by an unmanned aerial vehicle. The method comprises selecting a corresponding unmanned aerial vehicle low-altitude shooting scheme of traffic accident site according to whether three-dimensional site reconstruction or site animation simulation is needed; selecting and calculating shooting parameters of the unmanned aerial vehicle according to the unmanned aerial vehicle low-altitude shooting scheme selected; and shooting the traffic accident site according to the unmanned aerial vehicle low-altitude shooting scheme selected and the shooting parameters of the unmanned aerial vehicle, to obtain an aerial image sequence of the traffic accident site.

TECHNICAL FIELD

The present invention relates to the field of unmanned aerial vehicles,and more particularly, to an aerial image acquisition method and asystem for investigating a traffic accident site by an unmanned aerialvehicle.

BACKGROUND

According to a conventional method for investigating a road trafficaccident site, a traffic police mainly records the geometricalinformation of the accident site through distance measurement by ameasuring tool, observation and judgment, manual drawing and othersimple methods, so as to achieve the investigation purpose. Theseconventional methods have the defects of low efficiency, bad accuracyand incapability of conducting secondary verification to the accidentsite, and cannot meet the increasingly high requirement of people.However, strong judgment basis can be provided to liability judgment,reasonable analysis, settlement of insurance claim and judicialexpertise based on reappearance method of the live-action to the trafficaccident site, and more social value is generated. Therefore, usingvarious auxiliary investigation technologies to form a reappearableaccident site becomes the development trend of the road traffic accidentsite investigation.

According to different levels of information obtained, the road trafficaccident site investigation can be divided into two-dimensionalinvestigation and three-dimensional investigation. The traffic factorsof the accident site in actual application may not be on the same plane,which cannot meet the requirement of the two-dimensional investigationusually, and so as to cause a bigger error due to the two-dimensionalinvestigation; however, the three-dimensional investigation caneffectively reduce and basically eliminate this error, so as to reducethe effects of different traffic factors on the measurement results dueto the height reasons. The three-dimensional investigation can bedivided into a traffic accident site surveying and mapping technologyand a traffic accident three-dimensional reconstruction technologyaccording to the technical means and presenting modes.

The traffic accident site surveying and mapping technology refers toinvestigating and recording the information and status of the sitetraffic factors based on the actual site conditions, presenting theinformation and status by the accident site drawing mode, concerning theactual results only, and not concluding the accident reason and process.The traffic accident site surveying and mapping technology can also bedivided into a monocular camera investigation method and a multi-viewcamera investigation method according to the quantity of the surveyingand mapping cameras in the site. However, since the traffic accidentsite has uncertainty and it is difficult to calibrate the camera formultiple times in real time, the traffic accident site surveying andmapping technology still needs to be further improved on the aspect ofmeasurement accuracy.

The three-dimensional reconstruction technology of the traffic accidentsite comprises the three-dimensional reconstruction of site and processanimation simulation process. The three-dimensional reconstructionmethod of the traditional traffic accident site comprises a manualmeasuring method, a three-dimensional laser scanning method, andphotogrammetry, and the aerial camera can also be used to shoot the roadconditions from high altitude. The traditional manual measuring methodconsumes long time for drawing modeling, and the effects thereof havegreater difference with the actual conditions. Therefore, thetraditional manual measuring method can only be used for overviewreappearance of the site, and cannot show many details. Both thethree-dimensional laser scanning method and the photogrammetry requestthat equipment can measure around the accident site, but in this casethe movement efficiency is low, and the corresponding equipment which isrelatively heavy is generally loaded on a measuring car and cannotimplement around measurement on many sites. Helicopter shooting isusually used in current aerial shooting, which has the defects that arenot applied to the reconstruction of the road traffic accident site,including high shooting height, unapparent object feature and poormodeling effect. In addition, there are also researches on shooting thesite by an unmanned aerial vehicle currently, but only simple sitescanning shooting at a certain height is conducted, and only the generalpicture (i.e., site picture) of the site shot at an overlooked view canbe obtained. The actual view of the site cannot be shown inthree-dimension yet.

SUMMARY

In order to solve the technical problems above, an object of thedisclosure aims at providing an aerial image acquisition method forinvestigating a traffic accident site by an unmanned aerial vehicle withgood motility, high efficiency, comprehensiveness and high accuracy.

Another object of the disclosure aims at providing an aerial imageacquisition system for investigating a traffic accident site by anunmanned aerial vehicle with good motility, high efficiency,comprehensiveness and high accuracy.

The technical solution adopted in the disclosure is as follows.

An aerial image acquisition method for investigating a traffic accidentsite by an unmanned aerial vehicle, comprises the following steps of:

selecting a corresponding unmanned aerial vehicle low-altitude shootingscheme of traffic accident site according to whether three-dimensionalsite reconstruction or site animation simulation is needed, wherein theunmanned aerial vehicle low-altitude shooting scheme of traffic accidentsite includes but is not limited to a global-scope “S-shaped” itinerantvertical high-angle shooting scheme and a combined shooting scheme, andthe combined shooting scheme is formed by superimposing the global-scope“S-shaped” itinerant vertical high-angle shooting scheme with a partialthree-dimensional site multilevel surrounding inclined shooting scheme;

selecting and calculating shooting parameters of the unmanned aerialvehicle according to the unmanned aerial vehicle low-altitude shootingscheme selected; and

shooting the traffic accident site according to the unmanned aerialvehicle low-altitude shooting scheme selected and the shootingparameters of the unmanned aerial vehicle, to obtain an aerial imagesequence of the traffic accident site.

Further, the step of selecting a corresponding unmanned aerial vehiclelow-altitude shooting scheme of traffic accident site according towhether three-dimensional site reconstruction or site animationsimulation is needed comprises:

S11: judging whether three-dimensional site reconstruction or siteanimation simulation is needed to select a corresponding trafficaccident site, and implementing step S13 if three-dimensional sitereconstruction or site animation simulation is needed; otherwise,implementing S12;

S12: selecting the global-scope “S-shaped” itinerant vertical high-angleshooting scheme as the unmanned aerial vehicle low-altitude shootingscheme of traffic accident site; and

S13: selecting the combined shooting scheme as the unmanned aerialvehicle low-altitude shooting scheme of traffic accident site.

Further, the step of selecting and calculating shooting parameters ofthe unmanned aerial vehicle according to the unmanned aerial vehiclelow-altitude shooting scheme selected comprises:

S21: selecting and calculating the shooting parameters of the unmannedaerial vehicle according to the global-scope “S-shaped” itinerantvertical high-angle shooting scheme;

S22: judging whether the unmanned aerial vehicle low-altitude shootingscheme is the combined shooting scheme, and implementing step S23 if theunmanned aerial vehicle low-altitude shooting scheme is the combinedshooting scheme; otherwise, shooting the traffic accident site; and

S23: selecting and calculating the shooting parameters of the unmannedaerial vehicle according to the partial three-dimensional sitemultilevel surrounding inclined shooting scheme.

Further, the step S21 comprises:

setting a height H₀ and a shooting interval T₀ of an aerial camera ofthe unmanned aerial vehicle;

respectively calculating a projected length of a long side of the aerialimage on the ground and a projected length of a short-side of the aerialimage on the ground according to the height H₀ of the aerial camera ofthe unmanned aerial vehicle, a viewing angle of the camera and a ratioof the long side to the short side of the aerial image;

calculating a flight velocity V₀ of the aerial camera of the unmannedaerial vehicle according to the height H₀, the shooting interval T₀ andan overlap ratio of front and back images in a course direction;

calculating a horizontal flight course interval Do according to theheight H₀ and the overlap ratio of images on a horizontal intervalflight course; and

calculating shooting time T and a shooting image quantity S of a regionto be shot according to the shooting interval T₀, the flight velocity V₀and the horizontal flight course interval D₀, wherein a calculationformula of the shooting time T is:

${T = \frac{{a^{*}\left( {\left\lfloor \frac{b}{D_{0}} \right\rfloor + 1} \right)} + b}{V_{0}}},$and a calculation formula of the shooting image quantity S is:

${S = \left\lceil \frac{T}{T_{0}} \right\rceil},$wherein a and b are respectively a length of a flight course side and alength of a horizontal side of the region to be shot, and ┌ ┐ is asymbol rounding up to an integer.

Further, the step S23 comprises:

setting four heights H₁, H₂, H₃ and H₄ of a flight track of the unmannedaerial vehicle, four corresponding surrounding radiuses R₁, R₂, R₃ andR₄, and four corresponding flight velocities V₁, V₂, V₃ and V₄;

calculating four shooting angles θ₁, θ₂, θ₃ and θ₄ of the camera of theunmanned aerial vehicle according to the heights H₁, H₂, H₃ and H₄, andthe corresponding surrounding radiuses R₁, R₂, R₃ and R₄; and

calculating four shooting intervals D₁, D₂, D₃ and D₄ of the unmannedaerial vehicle according to the heights H₁, H₂, H₃ and H₄, thecorresponding surrounding radiuses R₁, R₂, R₃ and R₄, and thecorresponding flight velocities V₁, V₂, V₃ and V₄.

Further, the step of shooting the traffic accident site according to theunmanned aerial vehicle low-altitude shooting scheme and the shootingparameters of the unmanned aerial vehicle, to obtain an aerial imagesequence of the traffic accident site comprises:

S31: shooting the traffic accident site according to the global-scope“S-shaped” itinerant vertical high-angle shooting scheme and theshooting parameters of the unmanned aerial vehicle, to obtain ahorizontally-spaced photograph group at an overlooked view, wherein theaerial track of the unmanned aerial vehicle in global-scope “S-shaped”itinerant vertical high-angle shooting scheme is conducted in a“S-shaped” horizontally-spaced itinerant manner at a fixed height, theangle of the camera in the unmanned aerial vehicle is verticallydownward, and the unmanned aerial vehicle moves at a constant velocity;

S32: judging whether the unmanned aerial vehicle low-altitude shootingscheme selected is the combined shooting scheme, and implementing stepS33 if the unmanned aerial vehicle low-altitude shooting scheme selectedis the combined shooting scheme; otherwise, ending the acquisitionprocedure and using the horizontally-spaced photograph group shot at anoverlooked view as the aerial image sequence of the traffic accidentsite; and

S33: shooting the traffic accident site according to the partialthree-dimensional site multilevel surrounding inclined shooting schemeand the shooting parameters of the unmanned aerial vehicle, to obtain aphotograph group with different heights and different radiuses,combining the horizontally-spaced photograph group shot at an overlookedview and the photograph group with different heights and differentradiuses into the aerial image sequence of the traffic accident site,operating the unmanned aerial vehicle to fly above a target objectaccording to the partial three-dimensional site multilevel surroundinginclined shooting scheme firstly, and then shooting around the targetobject from top to bottom and from interior to exterior according to thefour heights H₁, H₂, H₃ and H₄, and the four surrounding radiuses R₁,R₂, R₃ and R₄ on the principle that the target object is located at aview finding center, to obtain four groups of photographs with fourheights and four radiuses.

Another technical solution adopted in the disclosure is as follows.

An aerial image acquisition system for investigating a traffic accidentsite by an unmanned aerial vehicle comprises:

a shooting scheme selector, configured to select a correspondingunmanned aerial vehicle low-altitude shooting scheme of traffic accidentsite according to whether three-dimensional site reconstruction or siteanimation simulation is needed, wherein the unmanned aerial vehiclelow-altitude shooting scheme of traffic accident site includes but isnot limited to a global-scope “S-shaped” itinerant vertical high-angleshooting scheme and a combined shooting scheme, and the combinedshooting scheme is formed by combining the global-scope “S-shaped”itinerant vertical high-angle shooting scheme with a partialthree-dimensional site multilevel surrounding inclined shooting scheme;

a parameter calibration module, configured to select and calculateshooting parameters of the unmanned aerial vehicle according to theunmanned aerial vehicle low-altitude shooting scheme selected; and

a site shooting module, configured to shoot the traffic accident siteaccording to the unmanned aerial vehicle low-altitude shooting schemeselected and the shooting parameters of the unmanned aerial vehicle, toobtain an aerial image sequence of the traffic accident site.

Further, the parameter calibration module comprises:

a first calibration circuit, configured to select and calculate theshooting parameters of the unmanned aerial vehicle according to theglobal-scope “S-shaped” itinerant vertical high-angle shooting scheme;

a first judgment circuit, configured to judge whether the unmannedaerial vehicle low-altitude shooting scheme is the combined shootingscheme, and swift to a second calibration circuit, if the unmannedaerial vehicle low-altitude shooting scheme is the combined shootingscheme; otherwise, swift to the site shooting module; and

a second calibration circuit, configured to select and calculate theshooting parameters of the unmanned aerial vehicle according to thepartial three-dimensional site multilevel surrounding inclined shootingscheme.

Further, the second calibration circuit, comprises:

a setting sub-circuit, configured to set four heights H₁, H₂, H₃ and H₄of a flight track of the unmanned aerial vehicle, four correspondingsurrounding radiuses R₁, R₂, R₃ and R₄, and four corresponding flightvelocities V₁, V₂, V₃ and V₄;

a first calculation sub-circuit, configured to calculate four shootingangles θ₁, θ₂ θ₃ and θ₄ of the camera of the unmanned aerial vehicleaccording to the heights H₁, H₂, H₃ and H₄, and the correspondingsurrounding radiuses R₁, R₂, R₃ and R₄; and

a second calculation sub-circuit, configured to calculate four shootingintervals D₁, D₂, D₃ and D₄ of the unmanned aerial vehicle according tothe heights H₁, H₂, H₃ and H₄, the corresponding surrounding radiusesR₁, R₂, R₃ and R₄, and the corresponding flight velocities V₁, V₂, V₃and V₄.

Further, the site shooting module comprises:

a first shooting circuit, configured to shoot the traffic accident siteaccording to the global-scope “S-shaped” itinerant vertical high-angleshooting scheme and the shooting parameter of the unmanned aerialvehicle, to obtain a horizontally-spaced photograph group at anoverlooked view, wherein the aerial track of the unmanned aerial vehiclein global-scope “S-shaped” itinerant vertical high-angle shooting schemeis conducted in a “S-shaped” horizontally-spaced itinerant manner at afixed height, the angle of the camera in the unmanned aerial vehicle isvertically downward, and the unmanned aerial vehicle moves at a constantvelocity;

a second judging circuit is configured to judge whether the unmannedaerial vehicle low-altitude shooting scheme selected is the combinedshooting scheme, implement step S33 if the unmanned aerial vehiclelow-altitude shooting scheme selected is the combined shooting scheme;otherwise, end the acquisition procedure and use the horizontally-spacedphotograph group shot at an overlooked view as the aerial image sequenceof the traffic accident site; and

a second shooting circuit, configured to shoot the traffic accident siteaccording to the partial three-dimensional site multilevel surroundinginclined shooting scheme and the shooting parameters of the unmannedaerial vehicle, to obtain a photograph group with different heights anddifferent radiuses, combine the horizontally-spaced photograph groupshot at an overlooked view and the photograph group with differentheights and different radiuses into the aerial image sequence of thetraffic accident site, operate the unmanned aerial vehicle to fly abovea target object according to the partial three-dimensional sitemultilevel surrounding inclined shooting scheme firstly, and then shootaround the target object from top to bottom and from interior toexterior according to the four heights H₁, H₂, H₃ and H₄, and the foursurrounding radiuses R₁, R₂, R₃ and R₄ on the principle that the targetobject is located at a view finding center, to obtain four groups ofphotographs with four heights and four radiuses.

The beneficial effect of the method according to the disclosure:comprises the corresponding unmanned aerial vehicle low-altitudeshooting scheme of traffic accident site according to whetherthree-dimensional site reconstruction or site animation simulation isneeded, and the steps of selecting and calculating shooting parametersof the unmanned aerial vehicle according to the unmanned aerial vehiclelow-altitude shooting scheme selected, and shooting the traffic accidentsite according to the unmanned aerial vehicle low-altitude shootingscheme selected and the shooting parameters of the unmanned aerialvehicle, and the aerial image sequence is collected by the unmannedaerial vehicle, which gives give consideration to both the convenienceand the motility; the unmanned aerial vehicle low-altitude shootingscheme of traffic accident site includes but is not limited to aglobal-scope “S-shaped” itinerant vertical high-angle shooting schemeand a combined shooting scheme, which not only can shoot the overallsituation through the global-scope “S-shaped” itinerant verticalhigh-angle shooting scheme to obtain the site drawing at an overlookedview, but also can obtain the surrounding shooting image sequence withdifferent angles and different levels through the partialthree-dimensional site multilevel surrounding inclined shooting schemein the combined shooting scheme, so as to realize multi-viewcomprehensive investigation to the traffic accident site, and providesufficient data for the three-dimensional reconstruction or the actualview of the animation simulation accident site, and morecomprehensively, the efficiency of obtaining evidence to the accidentscene and the motility are greatly increased; and the aerial imageacquisition is conducted by the unmanned aerial vehicle low-altitudeshooting scheme, the shooting height is low, the defects that thefeature of the aerial shooting object of helicopter is not obvious andthe effect of modeling is not good are overcame, and the accuracy ishigher.

The beneficial effect of the system according to the disclosure:comprises the shooting scheme selector, the parameter calibration moduleand the site shooting module, and the aerial image sequence is collectedby the unmanned aerial vehicle, which gives give consideration to boththe convenience and the motility; the unmanned aerial vehiclelow-altitude shooting scheme of traffic accident site includes but isnot limited to a global-scope “S-shaped” itinerant vertical high-angleshooting scheme and a combined shooting scheme, which not only can shootthe overall situation through the global-scope “S-shaped” itinerantvertical high-angle shooting scheme to obtain the site drawing at anoverlooked view, but also can obtain the surrounding shooting imagesequence with different angles and different levels through the partialthree-dimensional site multilevel surrounding inclined shooting schemein the combined shooting scheme, so as to realize multi-viewcomprehensive investigation to the traffic accident site, and providesufficient data for the three-dimensional reconstruction or the actualview of the animation simulation accident site, and morecomprehensively, the efficiency of obtaining evidence to the accidentscene and the motility are greatly increased; and the aerial imageacquisition is conducted by the unmanned aerial vehicle low-altitudeshooting scheme, the shooting height is low, the defects that thefeature of the aerial shooting object of helicopter is not obvious andthe effect of modeling is not good are overcame, and the accuracy ishigher.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall flow chart of an aerial image acquisition methodfor investigating a traffic accident site by an unmanned aerial vehicleaccording to the disclosure;

FIG. 2 is a schematic diagram of an aerial track of a combined shootingscheme of an unmanned aerial vehicle and a camera angle according to thedisclosure;

FIG. 3 is a top view of the aerial track of the combined shooting schemeof the unmanned aerial vehicle according to the disclosure;

FIG. 4 is a schematic diagram of the track of global-scope “S-shaped”horizontally-spaced vertical high-angle shooting by the unmanned aerialvehicle according to the disclosure;

FIG. 5 is a top view of the track of the global-scope “S-shaped”horizontally-spaced vertical high-angle shooting by the unmanned aerialvehicle according to the disclosure;

FIG. 6 is a schematic diagram of the track of partial multi-anglesurrounding inclined shooting by the unmanned aerial vehicle accordingto the disclosure; and

FIG. 7 is a top view of the track of the partial multi-angle surroundinginclined shooting by the unmanned aerial vehicle according to thedisclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, an aerial image acquisition method forinvestigating a traffic accident site by an unmanned aerial vehiclecomprises the following steps of:

selecting a corresponding unmanned aerial vehicle low-altitude shootingscheme of traffic accident site according to whether three-dimensionalsite reconstruction or site animation simulation is needed, wherein theunmanned aerial vehicle low-altitude shooting scheme of traffic accidentsite includes but is not limited to a global-scope “S-shaped” itinerantvertical high-angle shooting scheme and a combined shooting scheme, andthe combined shooting scheme is formed by superimposing the global-scope“S-shaped” itinerant vertical high-angle shooting scheme with a partialthree-dimensional site multilevel surrounding inclined shooting scheme;

selecting and calculating shooting parameters of the unmanned aerialvehicle according to the unmanned aerial vehicle low-altitude shootingscheme selected; and

shooting the traffic accident site according to the unmanned aerialvehicle low-altitude shooting scheme selected and the shootingparameters of the unmanned aerial vehicle, to obtain an aerial imagesequence of the traffic accident site.

In that case, only the site drawing at an overlooked view is neededwithout needing the three-dimensional site reconstruction or siteanimation simulation. At this point, only the photograph group shot bythe global-scope “S-shaped” itinerant vertical high-angle shootingscheme selected is needed to conduct quick modeling with low accuracy.Thus, the generated model can guarantee the modeling effect ofbird's-eye view, and the information of the outline and line canbasically satisfy the drawing requirement of the site drawing. Thethree-dimensional site reconstruction or site animation simulation isneeded, which means that the site drawing at an overlooked view and thesurrounding shooting image sequence with different angles and differentlevels are needed at the same time. At this point, the combined shootingscheme needs to be used: the photograph group shot by the global-scope“S-shaped” itinerant vertical high-angle shooting scheme selected isneeded to conduct quick modeling with low accuracy, and the surroundingshooting image sequence of the partial three-dimensional site multilevelsurrounding inclined shooting scheme is also needed to conduct thethree-dimensional site reconstruction with high accuracy or the siteanimation simulation with high accuracy.

The existing quadrotor unmanned aerial camera is preferably selected asthe unmanned aerial vehicle of the disclosure, and the air vehicle isprovided with a camera.

Further, as a preferred embodiment, the step of selecting acorresponding unmanned aerial vehicle low-altitude shooting scheme oftraffic accident site according to whether three-dimensional sitereconstruction or site animation simulation is needed comprises:

S11, judging whether three-dimensional site reconstruction or siteanimation simulation is needed to select a corresponding trafficaccident site, and implementing step S13 if three-dimensional sitereconstruction or site animation simulation is needed; otherwise,implementing S12;

S12, selecting the global-scope “S-shaped” itinerant vertical high-angleshooting scheme as the unmanned aerial vehicle low-altitude shootingscheme of traffic accident site; and

S13, selecting the combined shooting scheme as the unmanned aerialvehicle low-altitude shooting scheme of traffic accident site.

Further, as a preferred embodiment, the step of selecting andcalculating shooting parameters of the unmanned aerial vehicle accordingto the unmanned aerial vehicle low-altitude shooting scheme selectedcomprises:

S21, selecting and calculating the shooting parameters of the unmannedaerial vehicle according to the global-scope “S-shaped” itinerantvertical high-angle shooting scheme;

S22, judging whether the unmanned aerial vehicle low-altitude shootingscheme is the combined shooting scheme, and implementing step S23 if theunmanned aerial vehicle low-altitude shooting scheme is the combinedshooting scheme; otherwise, shooting the traffic accident site; and

S23, selecting and calculating the shooting parameters of the unmannedaerial vehicle according to the partial three-dimensional sitemultilevel surrounding inclined shooting scheme.

Further, as a preferred embodiment, the step S21 comprises:

setting a height H₀ and a shooting interval T₀ of an aerial camera ofthe unmanned aerial vehicle;

respectively calculating a projected length of a long side of the aerialimage on the ground and a projected length of a short-side of the aerialimage on the ground according to the height H₀ of the aerial camera ofthe unmanned aerial vehicle, a viewing angle of the camera and a ratioof the long side to the short side of the aerial image;

calculating a flight velocity V₀ of the aerial camera of the unmannedaerial vehicle according to the height H₀, the shooting interval T₀ andan overlap ratio of front and back images in a course direction;

calculating a horizontal flight course interval Do according to theheight H₀ and the overlap ratio of images on a horizontal intervalflight course; and

calculating shooting time T and a shooting image quantity S of a regionto be shot according to the shooting interval T₀, the flight velocity V₀and the horizontal flight course interval D₀, wherein a calculationformula of the shooting time T is:

${T = \frac{{a^{*}\left( {\left\lfloor \frac{b}{D_{0}} \right\rfloor + 1} \right)} + b}{V_{0}}},$and a calculation formula of the shooting image quantity S is:

${S = \left\lceil \frac{T}{T_{0}} \right\rceil},$wherein a and b are respectively a length of a flight course side and alength of a horizontal side of the region to be shot, and ┌┐ is a symbolrounding up to an integer.

Further, as a preferred embodiment, the step S23 comprises:

setting four heights H₁, H₂, H₃ and H₄ of a flight track of the unmannedaerial vehicle, four corresponding surrounding radiuses R₁, R₂, R₃ andR₄, and four corresponding flight velocities V₁, V₂, V₃ and V₄;

calculating four shooting angles θ₁, θ₂, θ₃ and θ₄ of the camera of theunmanned aerial vehicle according to the heights H₁, H₂, H₃ and H₄, andthe corresponding surrounding radiuses R₁, R₂, R₃ and R₄; and

calculating four shooting intervals D₁, D₂, D₃ and D₄ of the unmannedaerial vehicle according to the heights H₁, H₂, H₃ and H₄, thecorresponding surrounding radiuses R₁, R₂, R₃ and R₄, and thecorresponding flight velocities V₁, V₂, V₃ and V₄.

Further, as a preferred embodiment, the step of shooting the trafficaccident site according to the unmanned aerial vehicle low-altitudeshooting scheme and the shooting parameters of the unmanned aerialvehicle, to obtain an aerial image sequence of the traffic accident sitecomprises:

S31, shooting the traffic accident site according to the global-scope“S-shaped” itinerant vertical high-angle shooting scheme and theshooting parameters of the unmanned aerial vehicle, to obtain ahorizontally-spaced photograph group at an overlooked view, wherein theaerial track of the unmanned aerial vehicle in global-scope “S-shaped”itinerant vertical high-angle shooting scheme is conducted in a“S-shaped” horizontally-spaced itinerant manner at a fixed height, theangle of the camera in the unmanned aerial vehicle is verticallydownward, and the unmanned aerial vehicle moves at a constant velocity;

S32, judging whether the unmanned aerial vehicle low-altitude shootingscheme selected is the combined shooting scheme, and implementing stepS33 if the unmanned aerial vehicle low-altitude shooting scheme selectedis the combined shooting scheme; otherwise, ending the acquisitionprocedure and using the horizontally-spaced photograph group shot at anoverlooked view as the aerial image sequence of the traffic accidentsite; and

S33, shooting the traffic accident site according to the partialthree-dimensional site multilevel surrounding inclined shooting schemeand the shooting parameters of the unmanned aerial vehicle, to obtain aphotograph group with different heights and different radiuses,combining the horizontally-spaced photograph group shot at an overlookedview and the photograph group with different heights and differentradiuses into the aerial image sequence of the traffic accident site,operating the unmanned aerial vehicle to fly above a target objectaccording to the partial three-dimensional site multilevel surroundinginclined shooting scheme firstly, and then shooting around the targetobject from top to bottom and from interior to exterior according to thefour heights H₁, H₂, H₃ and H₄, and the four surrounding radiuses R₁,R₂, R₃ and R₄ on the principle that the target object is located at aview finding center, to obtain four groups of photographs with fourheights and four radiuses.

Wherein the shooting conducted in a “S-shaped” horizontally-spaceditinerant manner at a fixed height refers to itinerant shootingconducted by the unmanned aerial vehicle at a fixed height with“S-shaped” track and fixed horizontal interval (the requirement on theoverlap ratio of the horizontal interval flight course).

Referring to FIG. 2, an aerial image acquisition system forinvestigating a traffic accident site by an unmanned aerial vehiclecomprises:

a shooting scheme selector, configured to select a correspondingunmanned aerial vehicle low-altitude shooting scheme of traffic accidentsite according to whether three-dimensional site reconstruction or siteanimation simulation is needed, wherein the unmanned aerial vehiclelow-altitude shooting scheme of traffic accident site includes but isnot limited to a global-scope “S-shaped” itinerant vertical high-angleshooting scheme and a combined shooting scheme, and the combinedshooting scheme is formed by combining the global-scope “S-shaped”itinerant vertical high-angle shooting scheme with a partialthree-dimensional site multilevel surrounding inclined shooting scheme;

a parameter calibration module, configured to select and calculateshooting parameters of the unmanned aerial vehicle according to theunmanned aerial vehicle low-altitude shooting scheme selected; and

a site shooting module, configured to shoot the traffic accident siteaccording to the unmanned aerial vehicle low-altitude shooting schemeselected and the shooting parameters of the unmanned aerial vehicle, toobtain an aerial image sequence of the traffic accident site.

Further, as a preferred embodiment, the parameter calibration modulecomprises:

a first calibration circuit, configured to select and calculate theshooting parameters of the unmanned aerial vehicle according to theglobal-scope “S-shaped” itinerant vertical high-angle shooting scheme;

a first judgment circuit, configured to judge whether the unmannedaerial vehicle low-altitude shooting scheme is the combined shootingscheme, and swift to a second calibration circuit if the unmanned aerialvehicle low-altitude shooting scheme is the combined shooting scheme;otherwise, swift to the site shooting module; and

a second calibration circuit, configured to select and calculate theshooting parameters of the unmanned aerial vehicle according to thepartial three-dimensional site multilevel surrounding inclined shootingscheme.

Further, as a preferred embodiment, the second calibration circuitcomprises:

a setting sub-circuit, configured to set four heights H₁, H₂, H₃ and H₄of a flight track of the unmanned aerial vehicle, four correspondingsurrounding radiuses R₁, R₂, R₃ and R₄, and four corresponding flightvelocities V₁, V₂, V₃ and V₄;

a first calculation sub-circuit, configured to calculate four shootingangles θ₁, θ₂ θ₃ and θ₄ of the camera of the unmanned aerial vehicleaccording to the heights H₁, H₂, H₃ and H₄, and the correspondingsurrounding radiuses R₁, R₂, R₃ and R₄; and

a second calculation sub-circuit, configured to calculate four shootingintervals D₁, D₂, D₃ and D₄ of the unmanned aerial vehicle according tothe heights H₁, H₂, H₃ and H₄, the corresponding surrounding radiusesR₁, R₂, R₃ and R₄, and the corresponding flight velocities V₁, V₂, V₃and V₄.

Further, as a preferred embodiment, the site shooting module comprises:

a first shooting circuit, configured to shoot the traffic accident siteaccording to the global-scope “S-shaped” itinerant vertical high-angleshooting scheme and the shooting parameter of the unmanned aerialvehicle, to obtain a horizontally-spaced photograph group at anoverlooked view, wherein the aerial track of the unmanned aerial vehiclein global-scope “S-shaped” itinerant vertical high-angle shooting schemeis conducted in a “S-shaped” horizontally-spaced itinerant manner at afixed height, the angle of the camera in the unmanned aerial vehicle isvertically downward, and the unmanned aerial vehicle moves at a constantvelocity;

a second judging circuit is configured to judge whether the unmannedaerial vehicle low-altitude shooting scheme selected is the combinedshooting scheme, implement step S33 if the unmanned aerial vehiclelow-altitude shooting scheme selected is the combined shooting scheme;otherwise, end the acquisition procedure and use the horizontally-spacedphotograph group shot at an overlooked view as the aerial image sequenceof the traffic accident site; and

a second shooting circuit, configured to shoot the traffic accident siteaccording to the partial three-dimensional site multilevel surroundinginclined shooting scheme and the shooting parameters of the unmannedaerial vehicle, to obtain a photograph group with different heights anddifferent radiuses, combine the horizontally-spaced photograph groupshot at an overlooked view and the photograph group with differentheights and different radiuses into the aerial image sequence of thetraffic accident site, operate the unmanned aerial vehicle to fly abovea target object according to the partial three-dimensional sitemultilevel surrounding inclined shooting scheme firstly, and then shootaround the target object from top to bottom and from interior toexterior according to the four heights H₁, H₂, H₃ and H₄, and the foursurrounding radiuses R₁, R₂, R₃ and R₄ on the principle that the targetobject is located at a view finding center, to obtain four groups ofphotographs with four heights and four radiuses.

The disclosure is further described in detail hereinafter with referenceto the drawings and the embodiments.

Embodiment 1

The existing mature investigation method mainly comprises a method ofjointing the high-angle vertical aerial image and a method of aerialmodeling to big regions by inclined photography with multiple lenses.The aerial shooting needs to be conducted at a higher height on the sameplane by the two methods, which has bad motility, low efficiency,incomprehensiveness and low accuracy. For this purpose, in thecombination of the basic features of the quadrotor aerial camera (onekind of unmanned aerial vehicles) and the method of obtaining evidencefor the purpose of three-dimensional site reconstruction, the embodimentprovides an aerial image acquisition method for investigating a trafficaccident site by an unmanned aerial vehicle, the method formulatesdifferent aerial shooting tracks and shooting schemes at extremely lowaltitude regarding to the overall and partial situation. The aerialshooting investigation method is realized by the unmanned aerialvehicle, the efficiency of obtaining evidence of the accident site andmotility are greatly increased, the advantage of ground close-rangeshooting method is expanded to the air, the multi-view comprehensiveinvestigation is realized, and the application object of quicklygenerating the accident site drawing and conducting thethree-dimensional site reconstruction or the site animation simulationcan be realized in the combination of the computer software system. Inaddition, the method can also increase the accuracy of thethree-dimensional reconstruction measurement value by restraining thethree-dimensional calibration object in the site, and the specificmethod is that: the space relation in the modeling result is accuratelyrestrained in the combination of the three-dimensional calibrationobject or/and the measurement result of the traditional method of thesite ground staffs, and after the reasonable restraint is set and theerror is confirmed to reach an acceptable scope, that is the accidentsite drawing is drawn according to the spatial measurement result of themodeling site, the continuous site locking and the continuousmeasurement are not needed. After the aerial image sequence acquisitionof the traffic accident site in the embodiment is ended, the follow-upthree-dimensional site modeling, the site animation simulation and otheraccident analysis operations can be conducted according to the collectedaerial image sequence.

The design object of the overall shooting scheme shall be that theoverall top view diagram meets the completion of the plane investigationof the accident site. The important three-dimensional object (such asthe accident car or the main traffic element) needs to meet therequirement of multi-angle observation after the three-dimensionalreconstruction. The calibration object shall have the specific actualreference meaning in the modeling site (that is, the measurement valueof the reestablished site is compared with the ground investigationresult after the calibration object is restrained according to thereasonable ratio, and the actual reference value is needed). Therefore,the shooting scheme of the embodiment is designed with two basicshooting schemes: the first is a global-scope “S-shaped” itinerantvertical high-angle shooting scheme, and the second is the partialthree-dimensional site multilevel surrounding inclined shooting scheme.The two basic shooting schemes are superimposed to form the combinedshooting scheme of the disclosure, and the shooting method and theshooting angle of the camera are respectively shown in FIG. 2 and FIG.3. The two basic shooting schemes are described in detail as follows.

(I) The Global-Scope “S-Shaped” Itinerant Vertical High-Angle ShootingScheme.

Regarding to the global-scope shooting, the shooting method is as shownin FIGS. 4 and 5, the shooting is conducted according to the aerialtrack of the quadrotor unmanned aerial camera in a “S-shaped”horizontally-spaced itinerant manner at a fixed height, the angle of thecamera is vertically downward, and the quadrotor unmanned aerial cameramoves at a constant velocity. The overlap ratio O_(fa) of two photos atfront and back in the flight direction in going forward along a straightline shall keep more than 50% (i.e., O_(fa)>=50%), and the overlap ratioO_(lr) of two neighboring flight strips, i.e., photos on the flightdirection shall keep more than 60% (i.e., O_(lr)>=60%). Since the flightheight is relatively low, the image sequence obtained by this method ismainly related to the flight height, horizontal flight course interval,flight direction flight velocity and shooting interval. In order to meetmore than 50% superposition of images at front and back in the flightdirection and more than 60% superposition in the horizontal direction,the flight height H₀, the flight velocity V₀, the shooting interval T₀and the horizontal flight course interval D₀ need to be set. Regardingto the actual operation feasibility of the quadrotor unmanned aerialcamera, the flight height H₀ and the shooting interval T₀ are importantsetting parameters. Regarding to the camera of the quadrotor unmannedaerial camera, it is preferred to select 20 mm fixed focus wide-anglelens with about 94° visual angle, and considering the GPS error, theshaking of the quadrotor unmanned aerial camera, the deviation of theflight course and other actual conditions, the visual angle can besimplified to 90° for estimation, and the selection and calculationprocess of the corresponding shooting parameter specifically comprisesthe following contents.

(1) The flight height H₀=10 m and the shooting interval T₀=2s are set.

(2) If the calculation is conducted according to the ratio 4:3 of thelong and short sides of the aerial photo and the visual angle 90°, thecorresponding ground projection length of the long side of the aerialphoto is 2H₀, i.e., 20 m, and the corresponding ground projection lengthof the short side of the aerial photo is 1.5H₀, i.e., 15 m.

(3) In order to guarantee that the superposition degree of the images atfront and back in the flight direction is more than 50%, assuming thatthe flight direction does not have obvious deviation, and the quadrotorunmanned aerial camera forwardly flies along a straight line, the twoimages at front and back need more than 0.75H₀ superposition in theflight direction. Since the shooting interval T₀=2s, the flight velocityV₀ of the quadrotor unmanned aerial camera can be limited to be:

${0 < V_{0} \leq \frac{0.75H_{0}}{T_{0}}} = {3.75\mspace{14mu} m\text{/}{s.}}$

(4) In order to guarantee that the superposition degree of the images onthe horizontally-spaced flight course is more than 60%, assuming thatall the quadrotor unmanned aerial cameras are on the same level toshoot, the horizontal flight course interval D₀ shall meet:0<D₀≤1.2H₀=12 m.

(5) Regarding to the region to be shot with side length of the flightcourse a, the horizontal side length b, and the scope a*b, the shootingtime

${T = \frac{{a^{*}\left( {\left\lfloor \frac{b}{D_{0}} \right\rfloor + 1} \right)} + b}{V_{0}}},$and the shooting interval T₀=2s. Therefore, the shooting image quantity

$S = {\left\lceil \frac{T}{T_{0}} \right\rceil.}$Assuming that a=96 m and b=48 m, then

$T = {\frac{{96*4} + 48}{3.75} = {{115.2s\mspace{14mu}{and}\mspace{14mu} S} = 58.}}$

(II) The Partial Three-Dimensional Site Multilevel Surrounding InclinedShooting Scheme

Regarding to the partial three-dimensional site shooting scheme with thepurpose of the three-dimensional site reconstruction (i.e.,three-dimensional modeling or animation simulation), the shooting methodis that: the quadrotor unmanned aerial camera is operated to fly abovethe target object (comprising the car and the calibration object of thecheckerboard in front of the car), a central point is determined, andthen shooting is conducted in a surrounding and inclined manner aroundthe target object from top to bottom and from interior to exterioraccording to the four heights H₁, H₂, H₃ and H₄, and the foursurrounding radiuses R₁, R₂, R₃ and R₄ on the principle that the targetobject is located at a view finding center. According to differentheight of aerial track and the surrounding radius, the angle of thecamera (i.e., the included angles between an optical axis of the cameraand the perpendicular line of the ground: θ₁, θ₂, θ₃ and θ₄) is alsodistinguished. The shooting intervals D₁, D₂, D₃ and D₄ also need to bedetermined according to the designed flight heights H₁, H₂, H₃ and H₄,the surrounding radiuses R₁, R₂, R₃ and R₄ and the designed flightvelocities V₁, V₂, V₃ and V₄ in site operation. In order to reach thevisual requirement on site reconstruction, each height can be set ascollecting at least 32 images to meet the requirement on thethree-dimensional reconstruction.

The general shooting procedure of the partial three-dimensional sitemultilevel surrounding inclined shooting scheme is to enable thequadrotor unmanned aerial camera to shoot around the calibration objectin a surrounding manner, so as to obtain four groups of photos accordingto four heights and four radiuses. Moreover, in order to increase themodeling effect of the target region, after the embodiment using thequadrotor unmanned aerial camera to shoot the target region in asurrounding manner (i.e., the car and the calibration object of thecheckerboard in front of the car) to obtain four groups of photos, agroup of photos can also be additionally shot according to a largerradius at a lowest height in the four heights. That is to say, fivegroups of photos are obtained by the partial three-dimensional sitemultilevel surrounding inclined shooting scheme according to fourheights and five radiuses.

If setting H₁=11 m, R₁=5 m; H₂=9 m, R₂=7 m; H₃=7 m, R₃=9 m; H₄=5 m, R₄=5m; and H₄=5 m, R₅=11 m, the quantity of image through screening is shownin Table 1:

TABLE 1 Quantity of shooting photos of target object and target regionH₁ = 11 m H₂ = 9 m H₃ = 7 m H₄ = 5 m H₄ = 5 m R₁ = 5 m R₂ = 7 m R₃ = 9 mR₄ = 5 m R₅ = 11 m Target 44 40 51 82 — object Target 102 103 120 137128 region

It should be recognized that embodiments in the disclosure can beimplemented or embodied via computer hardware, a combination of bothhardware and software, or by computer instructions stored in anon-transitory computer-readable memory. The methods can be implementedin computer programs using standard programming techniques—including anon-transitory computer-readable storage medium configured with acomputer program, where the storage medium so configured causes acomputer to operate in a specific and predefined manner—according to themethods and figures described in this Specification. Each program may beimplemented in a high level procedural or object oriented programminglanguage to communicate with a computer system. However, the programscan be implemented in assembly or machine language, if desired. In anycase, the language can be a compiled or interpreted language. Moreover,the program can run on dedicated integrated circuits programmed for thatpurpose.

Further, the modules and circuits may be implemented in any type ofcomputing platform that is operatively connected to a suitabletomography data scanning device, including but not limited to, personalcomputers, mini-computers, main-frames, workstations, networked ordistributed computing environments, computer platforms separate,integral to, or in communication with charged particle tools or otherprocessing devices, and the like.

Comparing with the prior art, the disclosure has the followingadvantages

1) The image sequence is collected by the unmanned aerial vehicle, whichgives give consideration to both the convenience and the motility, canrealize multi-view comprehensive investigation, and provides full datafor three-dimensional reconstruction accident scene, so as to greatlyincrease the efficiency of obtaining evidence to the accident scene andthe motility.

2) The combined shooting scheme gives the track scheme in global serviceand partial shooting. That is, the “S-shaped” track scanning method isused in high-angle shooting, and the peripheral surrounding trackscanning with multiple heights and multiple radiuses is used in partialshooting, which is more comprehensive.

3) The image sequence acquisition method provided by the disclosure canbe flexibly applied: if the site drawing at an overlooked view is neededonly, only the photo group shot by the global-scope “S-shaped” itinerantvertical high-angle shooting scheme is needed to conduct quick modelingwith low accuracy. Thus, the generated model can guarantee the modelingeffect at a birds-eye view, and the basic information of the outline andthe line can meet the drawing requirement on the site drawing; and ifthe three-dimensional reconstruction with high accuracy or the siteanimation simulation with high accuracy needs to be conducted, thecombined shooting scheme is used.

4) The space relation in the modeling result is accurately restrained inthe combination of the three-dimensional calibration object or/and themeasurement result of the traditional method of the site ground staffs,and after the reasonable restraint is set and the error is confirmed toreach an acceptable scope, that is the accident site drawing is drawnaccording to the spatial measurement result of the modeling site, thecontinuous site locking and the continuous measurement are not needed,which is more convenient.

Although the preferred embodiments of the invention have beenspecifically described above, the invention is not limited thereto.Those skilled in the art can make various equivalent deformations orreplacements without departing from the spirit of the invention, andthese equivalent deformations or replacements shall fall into the scopedefined by the claims of the application.

The invention claimed is:
 1. An aerial image acquisition method forinvestigating a traffic accident site by an unmanned aerial vehicle,comprising the steps of: selecting a corresponding unmanned aerialvehicle low-altitude shooting scheme of traffic accident site accordingto whether three-dimensional site reconstruction or site animationsimulation is needed, the unmanned aerial vehicle low-altitude shootingscheme of traffic accident site including a global-scope “S-shaped”itinerant vertical high-angle shooting scheme and a combined shootingscheme, and the combined shooting scheme being formed by superimposingthe global-scope “S-shaped” itinerant vertical high-angle shootingscheme with a partial three-dimensional site multilevel surroundinginclined shooting scheme; selecting and calculating shooting parametersof the unmanned aerial vehicle according to the unmanned aerial vehiclelow-altitude shooting scheme selected, comprising: S21, selecting andcalculating the shooting parameters of the unmanned aerial vehicleaccording to the global-scope “S-shaped” itinerant vertical high-angleshooting scheme; S22, judging whether the unmanned aerial vehiclelow-altitude shooting scheme is the combined shooting scheme, andimplementing step S23 if the unmanned aerial vehicle low-altitudeshooting scheme is the combined shooting scheme, otherwise shooting thetraffic accident site; and S23, selecting and calculating the shootingparameters of the unmanned aerial vehicle according to the partialthree-dimensional site multilevel surrounding inclined shooting scheme;shooting the traffic accident site according to the unmanned aerialvehicle low-altitude shooting scheme selected and the shootingparameters of the unmanned aerial vehicle, to obtain an aerial imagesequence of the traffic accident site, wherein the step S21 comprises:setting a height H₀ and a shooting interval T₀ of an aerial camera ofthe unmanned aerial vehicle; respectively calculating a projected lengthof a long side of the aerial image on the ground and a projected lengthof a short-side of the aerial image on the ground according to theheight H₀ of the aerial camera of the unmanned aerial vehicle, a viewingangle of the camera and a ratio of the long side to the short side ofthe aerial image; calculating a flight velocity V₀ of the aerial cameraof the unmanned aerial vehicle according to the height H₀, the shootinginterval T₀ and an overlap ratio of front and back images in a coursedirection; calculating a horizontal flight course interval D₀ accordingto the height H₀ and the overlap ratio of images on a horizontalinterval flight course; and calculating shooting time T and a shootingimage quantity S of a region to be shot according to the shootinginterval T₀, the flight velocity V₀ and the horizontal flight courseinterval D₀, wherein a calculation formula of the shooting time T is:${T = \frac{{a^{*}\left( {\left\lfloor \frac{b}{D_{0}} \right\rfloor + 1} \right)} + b}{V_{0}}},$and a calculation formula of the shooting image quantity S is:${S = \left\lceil \frac{T}{T_{0}} \right\rceil},$ wherein a and b arerespectively a length of a flight course side and a length of ahorizontal side of the region to be shot, and ┌ ┐ is a symbol roundingup to an integer.
 2. The aerial image acquisition method forinvestigating a traffic accident site by an unmanned aerial vehicleaccording to claim 1, wherein the step of selecting a correspondingunmanned aerial vehicle low-altitude shooting scheme of traffic accidentsite according to whether three-dimensional site reconstruction or siteanimation simulation is needed comprises: S11, judging whetherthree-dimensional site reconstruction or site animation simulation isneeded to select a corresponding traffic accident site, and implementingstep S13 if three-dimensional site reconstruction or site animationsimulation is needed, otherwise implementing S12; S12, selecting theglobal-scope “S-shaped” itinerant vertical high-angle shooting scheme asthe unmanned aerial vehicle low-altitude shooting scheme of trafficaccident site; and S13, selecting the combined shooting scheme as theunmanned aerial vehicle low-altitude shooting scheme of traffic accidentsite.
 3. The aerial image acquisition method for investigating a trafficaccident site by an unmanned aerial vehicle according to claim 1,wherein the step S23 comprises: setting four heights H₁, H₂, H₃ and H₄of a flight track of the unmanned aerial vehicle, four correspondingsurrounding radiuses R₁, R₂, R₃ and R₄, and four corresponding flightvelocities V₁, V₂, V₃ and V₄; calculating four shooting angles θ₁, θ₂,θ₃ and θ₄ of the camera of the unmanned aerial vehicle according to theheights H₁, H₂, H₃ and H₄, and the corresponding surrounding radiusesR₁, R₂, R₃ and R₄; and calculating four shooting intervals D₁, D₂, D₃and D₄ of the unmanned aerial vehicle according to the heights H₁, H₂,H₃ and H₄, the corresponding surrounding radiuses R₁, R₂, R₃ and R₄, andthe corresponding flight velocities V₁, V₂, V₃ and V₄.
 4. The aerialimage acquisition method for investigating a traffic accident site by anunmanned aerial vehicle according to claim 1, wherein the step S23comprises: setting four heights H₁, H₂, H₃ and H₄ of a flight track ofthe unmanned aerial vehicle, four corresponding surrounding radiuses R₁,R₂, R₃ and R₄, and four corresponding flight velocities V₁, V₂, V₃ andV₄; calculating four shooting angles θ₁, θ₂, θ₃ and θ₄ of the camera ofthe unmanned aerial vehicle according to the heights H₁, H₂, H₃ and H₄,and the corresponding surrounding radiuses R₁, R₂, R₃ and R₄; andcalculating four shooting intervals D₁, D₂, D₃ and D₄ of the unmannedaerial vehicle according to the heights H₁, H₂, H₃ and H₄, thecorresponding surrounding radiuses R₁, R₂, R₃ and R₄, and thecorresponding flight velocities V₁, V₂, V₃ and V₄.
 5. The aerial imageacquisition method for investigating a traffic accident site by anunmanned aerial vehicle according to claim 3, wherein the step ofshooting the traffic accident site according to the unmanned aerialvehicle low-altitude shooting scheme and the shooting parameters of theunmanned aerial vehicle, to obtain an aerial image sequence of thetraffic accident site comprises: S31, shooting the traffic accident siteaccording to the global-scope “S-shaped” itinerant vertical high-angleshooting scheme and the shooting parameters of the unmanned aerialvehicle, to obtain a horizontally-spaced photograph group at anoverlooked view, wherein the aerial track of the unmanned aerial vehiclein global-scope “S-shaped” itinerant vertical high-angle shooting schemeis conducted in a “S-shaped” horizontally-spaced itinerant manner at afixed height, the angle of the camera in the unmanned aerial vehicle isvertically downward, and the unmanned aerial vehicle moves at a constantvelocity; S32, judging whether the unmanned aerial vehicle low-altitudeshooting scheme selected is the combined shooting scheme, andimplementing step S33 if the unmanned aerial vehicle low-altitudeshooting scheme selected is the combined shooting scheme; otherwise,ending the acquisition procedure and using the horizontally-spacedphotograph group shot at an overlooked view as the aerial image sequenceof the traffic accident site; and S33, shooting the traffic accidentsite according to the partial three-dimensional site multilevelsurrounding inclined shooting scheme and the shooting parameters of theunmanned aerial vehicle, to obtain a photograph group with differentheights and different radiuses, combining the horizontally-spacedphotograph group shot at an overlooked view and the photograph groupwith different heights and different radiuses into the aerial imagesequence of the traffic accident site, operating the unmanned aerialvehicle to fly above a target object according to the partialthree-dimensional site multilevel surrounding inclined shooting schemefirstly, and then shooting around the target object from top to bottomand from interior to exterior according to the four heights H₁, H₂, H₃and H₄, and the four surrounding radiuses R₁, R₂, R₃ and R₄ on theprinciple that the target object is located at a view finding center, toobtain four groups of photographs with four heights and four radiuses.6. The aerial image acquisition method for investigating a trafficaccident site by an unmanned aerial vehicle according to claim 4,wherein the step of shooting the traffic accident site according to theunmanned aerial vehicle low-altitude shooting scheme and the shootingparameters of the unmanned aerial vehicle, to obtain an aerial imagesequence of the traffic accident site comprises: S31, shooting thetraffic accident site according to the global-scope “S-shaped” itinerantvertical high-angle shooting scheme and the shooting parameters of theunmanned aerial vehicle, to obtain a horizontally-spaced photographgroup at an overlooked view, wherein the aerial track of the unmannedaerial vehicle in global-scope “S-shaped” itinerant vertical high-angleshooting scheme is conducted in a “S-shaped” horizontally-spaceditinerant manner at a fixed height, the angle of the camera in theunmanned aerial vehicle is vertically downward, and the unmanned aerialvehicle moves at a constant velocity; S32, judging whether the unmannedaerial vehicle low-altitude shooting scheme selected is the combinedshooting scheme, and implementing step S33 if the unmanned aerialvehicle low-altitude shooting scheme selected is the combined shootingscheme; otherwise, ending the acquisition procedure and using thehorizontally-spaced photograph group shot at an overlooked view as theaerial image sequence of the traffic accident site; and S33, shootingthe traffic accident site according to the partial three-dimensionalsite multilevel surrounding inclined shooting scheme and the shootingparameters of the unmanned aerial vehicle, to obtain a photograph groupwith different heights and different radiuses, combining thehorizontally-spaced photograph group shot at an overlooked view and thephotograph group with different heights and different radiuses into theaerial image sequence of the traffic accident site, operating theunmanned aerial vehicle to fly above a target object according to thepartial three-dimensional site multilevel surrounding inclined shootingscheme firstly, and then shooting around the target object from top tobottom and from interior to exterior according to the four heights H₁,H₂, H₃ and H₄, and the four surrounding radiuses R₁, R₂, R₃ and R₄ onthe principle that the target object is located at a view findingcenter, to obtain four groups of photographs with four heights and fourradiuses.
 7. An aerial image acquisition system for investigating atraffic accident site by an unmanned aerial vehicle, comprising: ashooting scheme selection module, configured to select a correspondingunmanned aerial vehicle low-altitude shooting scheme of traffic accidentsite according to whether three-dimensional site reconstruction or siteanimation simulation is needed, wherein the unmanned aerial vehiclelow-altitude shooting scheme of traffic accident site includes but isnot limited to a global-scope “S-shaped” itinerant vertical high-angleshooting scheme and a combined shooting scheme, and the combinedshooting scheme is formed by combining the global-scope “S-shaped”itinerant vertical high-angle shooting scheme with a partialthree-dimensional site multilevel surrounding inclined shooting scheme;a parameter calibration module, configured to select and calculateshooting parameters of the unmanned aerial vehicle according to theunmanned aerial vehicle low-altitude shooting scheme selected, whereinthe calibration module comprises: a first calibration circuit,configured to select and calculate the shooting parameters of theunmanned aerial vehicle according to the global-scope “S-shaped”itinerant vertical high-angle shooting scheme; a first judgment circuit,configured to judge whether the unmanned aerial vehicle low-altitudeshooting scheme is the combined shooting scheme, and swift to a secondcalibration circuit if the unmanned aerial vehicle low-altitude shootingscheme is the combined shooting scheme; otherwise, swift to the siteshooting module; and a second calibration circuit, configured to selectand calculate the shooting parameters of the unmanned aerial vehicleaccording to the partial three-dimensional site multilevel surroundinginclined shooting scheme; and a site shooting module, configured toshoot the traffic accident site according to the unmanned aerial vehiclelow-altitude shooting scheme selected and the shooting parameters of theunmanned aerial vehicle, to obtain an aerial image sequence of thetraffic accident site, wherein the second calibration circuit comprises:a setting sub-circuit, configured to set four heights H₁, H₂, H₃ and H₄of a flight track of the unmanned aerial vehicle, four correspondingsurrounding radiuses R₁, R₂, R₃ and R₄, and four corresponding flightvelocities V₁, V₂, V₃ and V₄; a first calculation sub-circuit,configured to calculate four shooting angles θ₁, θ₂, θ₃ and θ₄ of thecamera of the unmanned aerial vehicle according to the heights H₁, H₂,H₃ and H₄, and the corresponding surrounding radiuses R₁, R₂, R₃ and R₄;and a second calculation sub-circuit, configured to calculate fourshooting intervals D₁, D₂, D₃ and D₄ of the unmanned aerial vehicleaccording to the heights H₁, H₂, H₃ and H₄, the correspondingsurrounding radiuses R₁, R₂, R₃ and R₄, and the corresponding flightvelocities V₁, V₂, V₃ and V₄.
 8. The aerial image acquisition system forinvestigating a traffic accident site by an unmanned aerial vehicleaccording to claim 7, wherein the site shooting module comprises: afirst shooting circuit, configured to shoot the traffic accident siteaccording to the global-scope “S-shaped” itinerant vertical high-angleshooting scheme and the shooting parameter of the unmanned aerialvehicle, to obtain a horizontally-spaced photograph group at anoverlooked view, wherein the aerial track of the unmanned aerial vehiclein global-scope “S-shaped” itinerant vertical high-angle shooting schemeis conducted in a “S-shaped” horizontally-spaced itinerant manner at afixed height, the angle of the camera in the unmanned aerial vehicle isvertically downward, and the unmanned aerial vehicle moves at a constantvelocity; a second judging circuit is configured to judge whether theunmanned aerial vehicle low-altitude shooting scheme selected is thecombined shooting scheme, implement step S33 if the unmanned aerialvehicle low-altitude shooting scheme selected is the combined shootingscheme; otherwise, end the acquisition procedure and use thehorizontally-spaced photograph group shot at an overlooked view as theaerial image sequence of the traffic accident site; and a secondshooting circuit, configured to shoot the traffic accident siteaccording to the partial three-dimensional site multilevel surroundinginclined shooting scheme and the shooting parameters of the unmannedaerial vehicle, to obtain a photograph group with different heights anddifferent radiuses, combine the horizontally-spaced photograph groupshot at an overlooked view and the photograph group with differentheights and different radiuses into the aerial image sequence of thetraffic accident site, operate the unmanned aerial vehicle to fly abovea target object according to the partial three-dimensional sitemultilevel surrounding inclined shooting scheme firstly, and then shootaround the target object from top to bottom and from interior toexterior according to the four heights H₁, H₂, H₃ and H₄, and the foursurrounding radiuses R₁, R₂, R₃ and R₄ on the principle that the targetobject is located at a view finding center, to obtain four groups ofphotographs with four heights and four radiuses.